The role of a thrust reverser during landing of an airplane is to improve the braking capacity of the airplane by reorienting at least part of the thrust generated by the turbojet engine forward. In this phase, the reverser obstructs the jet nozzle of the gases and orients the jet stream from the engine toward the front of the nacelle, thereby generating a counter-thrust added to the braking of the airplane's wheels.
The means implemented to perform this reorientation of the stream vary depending on the type of reverser. However, in all cases, the structure of a reverser comprises mobile cowls that can be moved between, on the one hand, a deployed position in which they open a passage in the nacelle intended for the deviated stream, and on the other hand, a retracted position in which they close the passage. These mobile cowls can also perform a bypass function or simply an activation function for other bypass means.
In grid reversers, for example, the mobile cowls slide along rails so that by pulling back during the open phase, they reveal grids of bypass vanes arranged in the thickness of the nacelle. A system of connecting rods connects said mobile cowl to locking doors that deploy inside the exhaust duct and block the output in direct flow. In door reversers, on the other hand, each mobile cowl pivots so as to block the stream and deviate it, and is therefore active in said reorientation.
In general, these mobile cowls are actuated by hydraulic or pneumatic cylinders that require a grid for conveying a pressurized fluid. This pressurized fluid is traditionally obtained either by air bleed on the turbojet engine in the case of a pneumatic system, or by withdrawal on the hydraulic circuit of the airplane. However, such systems require significant maintenance because the slightest leak in the hydraulic or pneumatic grid can have harmful consequences both on the reverser and on other parts of the nacelle. Furthermore, due to the reduced available space in the forward frame of the reverser, the placement and the protection of such a circuit are particularly delicate and bulky.
To offset the various drawbacks related to the pneumatic and hydraulic systems, the builders of thrust reversers have sought to replace them and equip their electromechanical actuator reversers as much as possible, lighter and more reliable. Such a reverser is described in document EP 0 843 089.
The reliability and availability of such electrical systems are important considerations and constitute an important development area for electrical actuating systems.
Despite the advances in this field, in particular owing to synchronization methods, and breakdown, incident and other management, thrust reverser devices are still considered braking assistance devices and are not certified as completely separate braking systems. In fact, the braking function is a primary function that must have a breakdown likelihood below 10−7 per hour of flight for aeronautic certifications and not a secondary function for which the breakdown likelihood can be greater.
A need therefore exists for a thrust reversal system allowing greater availability and greater reliability of the system.
The availability criterion refers to the capacity for the thrust reversal system to be deployed in order to fulfill its braking assistance function.
The reliability is the measurement of the operating or breakdown likelihood of a system used under particular conditions and for a given time. In aeronautics, this size characterizes the operating security of equipment.
One solution to improve the availability of a system is to increase the reliability of its components.
However, aeronautic equipment is already being developed to have optimal reliability and there is a need for an architectural solution making it possible to further improve this availability and reliability.